Process for making diolefins



Patented May 27, 1947 UNITED STATES PATENT OFFICE raocnss roa MAKING monar'ms Walter J. 'Ioussalnt, South Charleston, and-lease T. Dunn, Charleston. W. Va, asilgnora to Carbide and Carbon Chemicals Corporation, a corporation oi New York No Drawing. Application sass-mar a. 1942,

Serial m. 400,120

20 Claims. (on. zoo-cs1) The subject of this invention is a, process for making oleiines, and it more particularly relates to a process for making dienes. such as 1,3- butadiene.

Processes for making 1,3-butadiene wherein ethanol and acetaldehyde are passed over certain of the crotonaldehyde is readily reduced by the catalytic formation of butadiene, acetaldehyde and water to a pointlowenough so that acetaldehyde, which is a product of the butadiene dehydration catalysts are known. Modifications a process is disclosed for making 1,3-butadiene or its homologs by passing crotonaldehyde or its homologs with an alcohol, such as ethanol, in the vapor state over heated silica gel. The over-all reaction which occurs may be represented as follows: H.c-Ch= h.-cno+c,n.0n

iirotonaldehyde I Ethanol V nic'=cncn =on h.o-ono+mo Butadiene Aoetaldehyde Water According to the present invention, certain other catalysts are used for the same or similar reactions and they are found to be sufllciently active to operate satisfactorily at low concentrations of crotonaldehyde, as well as at higher concentrations of crotonaldehyde. Probably because of their greater activity, the catalysts of this invention are also effective when the crotonaldehyde itself is not fed to the reaction zone. but in its place an aldehyde capable of condensing to crotonaldehyde is used. For example, silica gel is capable of converting crotonaldeh'yde and ethanol'to butadiene, acetaldehyde and water. It is also capable of forming crotonaldehyde from acetaldeliyde. In the reaction involving the formation of butadiene from crotonaldehyde and ethanol in the presence of silica gel, it is usually iound that the concentrations of crotonaldehyde, acetaldehyde and water vapor are suchthat the acetaldehyde formed from the ethanol .is not converted to crotonaldehyde, but instead crotonaldehyde is converted to some extent to acetaldehyde. Also, if acetaldehyde, nather than crotonaldehyde, is fed along with QHdhol over heated silica gel some crotonaldehy Fit formed, but its conforming reaction, is converted to crotonaldehyde. These conclusions are based on the observed results that less 'aceta'ldehyde is found in the effluent reaction products than would be accounted for by the ethanol consumed: and that more butadiene is formed than would be expected from the original crotonaldehyde introduced. Also, if

acetaldehyde instead of crotonaldehyde is passed with ethanol over the catalysts of the present invention, a good yield of butadiene is obtained, in contrast to the results observed with silica gel, or with thecatalysts of the prior art.

This over-all reaction may be represented as follows: e

mc-cmouunc-cno Ethanol Acetaldahyde n.c=cu-cn=cn.+2n.o

Butadiene Water The catalysts of this invention consist of the group of sirconlum oxide, tantalum oxide, columbium oxide and combinations oi these oxides with silica: These combinations may be in the form of the silicates of zirconium, tantalum or columbium, or they may consist .of silica gel promoted by admixture with one or more of the oxides of these metals. 7 This latter embodiment is the prev ferred form of the catalyst.

centration is so low that Every smalL amount of l to form butadiene, acetaldehyde and water.

In the presence of these catalysts, crotonaldehyde and ethanol react at a suitable temperature It is believed that this is the essential reaction occurring even when acetaldehyde, rather than crotonaldehyde, is fed with the ethanol, although only small amounts of crotonaldehyde are found to be present .in the reaction products, and it may exist as a transitory intermediate largely in the adsorbed form on the catalyst. The reasons for concluding that crotonaldehyde'is an important intermediate are that the catalysts are found to be capable of forming crotonaldehyde from acetaldehyde rapidly at the temperature of the reaction in the absence of ethanol, and that they are also found capable of rapid conversion of crotonaldehyde and ethanol into butadiene, acetaldehyde and water.

In general, substituted crotonaldehydes, including-ketones, formed by substituting the aidehydic hydrogen atom, may be expected to react similarly to crotonaldehyde, provided that they are capable of rearranging to an enoi form. In

general, compounds which are capable oi ketcenol tautomerism contain a labile hydrogen atom attached to a carbon atom which is attached to a carbonyl group. Also, in place acetaldehyde, other carbonyl compounds capable oi. condensation to homologs of orotcnaldehyde may be employed.

Thus, the formation of 1,1-dimethyl butadiene from acetone and isopropanol has been indicated,

presumably through the intermediate formation 1 mesityl oxide. To the extent that they condense with each other, mixtures of vn hcnyl compounds may be employed to yield dienes containing the same number of carbon atoms as the sum of the carbon atoms 01' the carbonyl compounds. Thus, isoprene in association with other diene's may be iormed when mixtures of acetaldehyde and propionaldehyde are reacted with-ethanol in the presence of the catalysts of this invention.

On the other hand, when the carbonyl compounds contain at least i'our carbon at01115t d an oleflnic bond coniugaied with the carbonyl group, they react with primary and secondary alcohols in the presence of the catalysts at this invention to yield conjugated dienes oi the same number of carbon atoms as the carbonyl compounds introduced, and only small amounts of higher hydrocarbons are formed. 1

The distinctive characteristic of the catalysts of this invention, as compared with silica gel, is that they tend to a much greater degree to give dienes when saturated aldehydes-which are condensable to higher aldehydes together with an alcohol are passed over them. In those instances where the simple, direct reaction of the saturated aldehyde with the alcohol is relatively slow, a diene, rather than a mono-oleflne, is obtained in excellent yield. This is what occurs with metaldehyde.

Therefore, it is to be presumed that, if the aldehyde reacts readily with the alcohol on the catalyst surface, a hydrocarbon of the same number of carbon atoms as the aldehyde will be obtained. However. if the rate of this reaction is exceeded by the rate of condensation of the aldehyde -to a higher unsaturated aldehyde and by the rate of reaction or the latter with the alcohol, then a conjugated diene will be obtainedrhaving twice as many carbon atomsiasthe original aldehyde. The yields of the various possible products will be determined by the pertinent reaction velocities. I

The alcohol employed in any of these reactions may be any alcohol capable of dehydrogenation to a carbonyl compound, and this comprises the class of primary and secondary alcohols. Despite ,the fact that secondary alcohols show as much or even greater reactivity than primary alcohols, it is usually more desirable to employ an alcohol which is capable of being converted to a carbonyl compound identical to that introduced.

In the practice of this reaction, it is found that some unavoidable side-reactions occur, particularly the formation of high-boiling condensation products from thealdehydes and of low-boiling olefl'nes by dehydration of the alcohols. The proportion of aldehyde to alcohol is adjusted to minimize these reactions as is shown by the examples.

One of the more important industrial applications of the invention is the conversion of ethanol and acetaldehyde to butadiene, whichis' a valuable intermediate in the production of synthetic rubber. In practice, ethanol is the ultimate raw material, since ethanol may be readily dehydrogenated over a copper catalyst to yield l i i r acetaldehyde. Also, in commerciahoperation, the ethanol may contain a small amount of water. The mixture from this reaction, containing ethanol, acetaldehyde, water and hydrogen, along with recycled ethanol and acetaldehyde, the proportions belngadiusted so that the final mixture contains about 8 mols of ethanol per mo] the butadien'e converter.

The reaction products from thebutadiene converter are condensed at a temperature low,

enough, or a pressure high enough, to condense the butadiene, which boils at, -4 .5 ,C., and the liquid condensate isiractionally distilled to separate the butadiene from the ethanol, acetaldehyde, water and impurities formed in the 'reaction. The ethanol, acetaldehyd and low boiling lated in undesirable amounts.

impurities are: separated from the water and high boiling impuritifisi and lfccyqlcd through the buta- 'diene converter, 'Bartjorall oi the -ethanol may be recycled through the acetaldehyde converter. The low boilingimpurities include diethyl ether, ethyl acetate and butyraldehyde and a batch still may be provided for the removal of such impurities from the system when they havaaccumu- The butadiene traction asobtained even by eflicient distillation contains a small amount-oi impurities which are removable by other processes. Acetaldeh yde is present, since it forms an azeotropic with butadiene. The Metaldehyde can passage over the catalyst. The other impurities in the butadiene fraction are the ,butylen'e's and normal butane. Since their boiling points are very close to that of butadiene, it is diflicult to remove them by simple-fractional distillation. They can be removed, however; by distilling the butadiene fraction in the presence of a selective ,solvent for butadiena'such as dichlor'ethyl ether.

The, temperature cliche olcilne-iorming reac- Itions may vary from about 1'50v c, to about 400 c. to 450? c., depending on the activity of the catalystand the carbonyl-compound being re-.

acted. With acetaldehyde and ethanol, temperatures 0f about300 C. to 400 are preferable. Within these ranges, somewhat lower temperaturesare deslrable-whenoperating with carbonyl com ound in which an oleflne bone i conjugated with the carbonyl group or when using secondary alcohols. 'IIheuse of pressure may increase the speed of the reaction somewhat, but the proces: can economically be carried out at pressures in suflicient to compensate for the pressure drop removed and recovered for re- ,a aasei a of these decomposable salts. The nitrate is an ln.aqueous jcitric acid, and then impregnating silicagel with this solution and evaporating the water. ,fI'his mixture was placed in a stainless effective salt for this purpose when catalysts containing zirconium oxide are to be prepared, and

the citrates and oxalates give good results in the case of catalysts promoted with tantalum and columbium oxides.

The examples to follow will serve to illustrate the invention Example 1 A promoted silica gel catalyst was prepared by alternately digesting silica gel 'with nitric acid and washing it with water. The purified silica gel was then treated with an aqueous solution of zirconium nitrate and, after drying, ,thdacatalyst was heated at about 350 C. The heat treatment decomposed the zirconium nitrate to the oxide. and resulted in a catalyst impregnated with about 2% of zirconium oxide.

The catalyst was placed in a stainless steel tube and a mixture of ethanol and acetaldehyde in the molar ratio of 2 to 1, and containing about 8% by weight of water waspassed through the catalyst bed ata temperature 01' 330' C. .Based on the acetaldehyde introduced, a' 47% single-pass yield of the butadiene fraction 'wasobtained which contained about 93% by weight of bumdiene. The chlef impurities in this fraction, as in corresponding fractions 01' subsequent examples, were acetaldehyde and the normal butylenes.

' Example 2 A promoted silica gel catalyst was prepared by dissolving freshly precipitated columbic, acid steel and heated in .a current of iii-at a 7 temperature oifaboutaim" C. resultedin the oxidation of the organic residue of the acid leaving a deposit of about 2% by weight or columbium oxide on the catalyst.

mixture of ethanol and acetaidenyde'ifi the mom-I us :12 to 1, and containing about a'% by weight of water. was passed through the cata lyst bfldet'330i2. at a rate of about 4 mols' of reactants per. liter of catalyst per hour. The

Example 3 Apromoted silica gel catalyst was preparedby 6Q fled silica gel with this-solution and evaporating the water. This mixture was placed in astainhyde introduced.- The butadiene content of the fraction was about A commercial sample'oi zirconium silicate of a high degreeoi purity was mixed with water to form a paste and spread on a glass surface for drying. While the-paste'was still moist it was divided into pellets and these were then dried further. About 350 c." c. of these pellets were placedin a glass tube having an inside diameter o'f'one inch containing a small tube for a thermoco'uple disposed along its axis. The tube was then heated in an electric furnace to 320? to 330 C.

{A mixture containing 3.1 mols of ethanol, 1.45

"mols oi acetagldehyde and 0.-8 mol or water was 'Id at a rate-oi about60 c. c, of liquid per hour into-a vaporizerfand the vapors were passed through the' catalyst bed. The products of the reaction were collected and fractionally distilled.

kfractipn r 25.6 gran s ofmaterial boiling between --6" and 0 C. WasDbtained. This fraction contained 914m or butadiene. The total singlepass yield of the butadiene fraction based on the acetaldehyde consumed was about Emmiple 5 Dalma ia precipitated by add- 'i ng faqueousj ammonia to an aqueous solution of zirconium nitrate. The precipitate was washed and partly dried, and then cut into pellets which were further dried. The pellets were heated to 340 C., resulting in the formation of zirconium oxide. V

5 Ethanol andacetaldehyde in, the mom ratio lof 2 to 1, along with 8%'b'y weight of water, were the decompositions: the. caiummum curate and- 5 passed through v the catalyst at this temperature. in thisinstance, the single-pass yield of the butadiene fraction was 21%, based on the acetaldehyde introduced, and the butadiene content of the fraction was about 90%.

same 6 'A zirconium silicate catalyst was prepared as described in Exarhple l: A mixture of ethanol and crotonaldehyd'e in the molar ratio of 2 to 1, and'cohta lning' about 'Bto 9% water, was vaporized and passed through about 300 c. c. of theoatalyst at 3310 0.. and at a rate of about 4 mois per liter of catalyst perhour. Based on the crotonaldehyde introduced. a 49% single-pass yiel'r'i of the butadiene fraction was obtained, and

the butadiene content of the fraction was 95%.

' Example LA zirconiumioxide' catalyst was prepared as "described in Example 5. A mixture 01' ethanol less steel tube and heated in a currentof .air at U5 talum oxide on the catalyst.

i A mixture of ethanol and acetaldehydeinthe molar ratio oil to 1,'containing about 8% by weight of water; was passed through the catalyst bed at 350 C. The single-pass yield of-butadlene fraction amounted to 67% based on the acetalde 75,

and crotonaldehydein the molar ratio or 2 to 1, and 'eontaining'about 8 to 9% water, was vaporized and fed through about 300 c. c. oi the catalyst "at a temperature of 320 0., and at a rate of about 4111015 of reactants per liter of catalyst per hour. Based on the crotonaldehyde introduced, a 30% single-pass yield of the'butadiene fraction, containing butadiene, was obtained.

5. Example? A commercial sample of tantalum oxide containing 21%..otcolumbium oxide was supported .on. .ceramic ally 1 bonded fused aluminum oxide. The-amountof active catalyst on the support "amounted to 10% by. weight. Ethanol and cro- .tonaldehydelnvthe molar ratio of '2to 1, and containi'ng about 8. to 9% by weight or water, were vaporized and led through about 300 c. c. o! the catalyst at a temperature of 880' C. at a rate of about 4 mols of reactants per liter catalyst per hour. Based On the crotonaldehyde introduced, a 20% single-pass yield of butadiene traction containing 83% by weight of butadiene was obtained.

Example 9 A mixture or. 12.8 mole of ethanol and 4.22 mole of acetaldehyde, containing about 7% by weight of water. was vaporized at a rate or about 150 c. c. of the liquid mixture per hour. The vapors were passed into a catalyst chamber at 830 0., containing 325 c. c. of silica sel promoted with about 0.5% by weight of tantalum oxid The products of the reaction were collected separated by tractional distillation and analyzed. The recovered materials contained 9.54 mols of ethanol. 2.36 mois of acetaldehyde and 1.54 mols o1 butadlene. In addition, there was a small amount of material boiling between 9 and 95 C. with water which was not positivel identified. There was also a small amount of oil-like residue'boilinx above Considering that the ethanol and acetaldehyde consumed are equivalents in the eflicient production of butadiene, the following table lists the percentase of consumed ethanol and acetaldehyde which were converted to the products listed below: a

Per cent Butadiene 60.2 Butylene 2.4 Ethylene and propylene 8.5 Unidentified material (B. P. 9-95 (3., I111.) 12.2 Oil, boiling above 95 C 4.! Unaccounted for and carbon on the catalyst I 12.0

Total 100.0

Example 10 A ,zirconia promoted catalyst was prepared by decomposing 12 grams of zirconium nitrate im- .product was 0.26. If butadiene had been formed only by the reaction of the crotonaldehyde introduced with the ethanol, approximately equal molar amounts of acetaldehyde and butadiene in the reaction products would have been expected.

Example 11 This experiment illustratesthe preparation of butadiene directly from ethanol. Specially denatured ethanol containing about 8% water and a trace of acetaldehyde as a denaturant were passed over a reduced copper catalyst supported on ceramically bonded fused aluminum oxide at a temperature of 220 to 265 C. The mixture from this converter containing ethanol and acetaldhydein a molar ratio '0! about 2 to 1, along with water and hydrogen, was passed directly into a butadiene converter containing a silicagel catalyst promoted with about 0.5% of tantalum oxide. The reaction products from the butadiene converter were separated and identified. The results or the run are tabulated below:

Materials ylene 0.1 Elli... dioxi 3 0.2%-

Total, g

Conditions and Results:

Duration, hours t Single-pass yield of tedious from ethanol, per n a can dinfi lepass yield of unreacted acetaldehyde from et moi, per cent Prodl :l/glhm rate, z. oi butadiene/iitcr of gel oatays our Accounting of ethanol plus soetaldehyde consumed,

Oar non catalyst .I: Unidentified materials (B. P. H5 0.

While the above examples are intended to illustrate preferred methods of practicing the invention, it is to be understood that modifications of the reaction conditions are permissible. For instance, the molar ratio of the reactants may be varied widely, although an excess 01 the alcohol is preferred. Similarly, the space velocity of the reactants is not critical so far as is known and may be varied considerably from the values shown. Similarly, the amount of zirconium, tantalum' or columbium oxides on the promoted silica gel catalyst may be varied depending on the activity of the catalyst desired. In normal practice, these amounts might vary from about 0.1% to about 5%. As indicated in the abdve examples, silica gel promoted with tantalum oxide is the preferred catalyst. The addition of a small amount of columbium oxide to this preferred catalyst appears to enhance its activity and selectivity somewhat. While the catalysts of this invention vary in the yield of fourcarbon-atom hydrocarbons which they produce, they are all characterized by their selectivity in promoting a very high content of butadiene in this fraction. In this property, the catalysts are to be sharply distinguished from those of the prior art.

We claim:

1. Process for making dienes which comprises,

passing an acyclic mono-oiefinic aldehyde having at least four carbon atoms and a monohydric alcohol havin at least one hydrogen atom attached to the carbinol carbon atom over a catalyst of the group consisting of the oxides and silicates of zirconium, -tantalum, and columbium, and recovering a diene from the reaction products.

2. Process for making dienes which comprises passing a vaporous mixture,- containing an acyclic mono-olefinic aldehyde havine. at least [our carbon atoms and a monohydric alcohol having at least one hydrogen atom attached to the carblnol carbon atom, over a catalyst comprising silica gel promoted with zirconium oxide.

3. Process for making dienes which comprises passing a vaporous mixture, containing an acyclic mono-olefinic aldehyde having at least four carbon atoms and a monohydric alcohol having at least one hydrogen atom attached to the carbinol carbon atom, over a catalyst comprislngsilica gel promoted with tantalum oxide. i 4. Process for making dienes which comprises passing a. vaporous mixture, containing an acyclic mono-olefinic aldehyde having at least four carbon atoms and a monohydric alcohol having at least one hydrogen atom attached to the carhinol carbon atom, over a catalyst comprising silica gel promoted with co umblum oxide.

5. Process for making dienes which comprises passing a vaporous mixture, containing a saturated imonocarbonyl compound having from two ito three carbon atoms and a monohydric alcohol having from two to three carbon atoms, over a catalyst of the group consisting of the oxides and silicates of zirconium, tantalum and columbium, and recovering a dienefhaving from four to six carbon atoms from the reaction products.

6.Pl'0C8SS for 'making dienes which comprises passing a vaporous mixture, containing" a saturated monocarbonyl compound having from two to three carbon latoms and a monohydric alcohol having from two to three carbon atoms, over a catalyst comprising silica gel promoted'with zirconium oxide, and recovering a diene having from four to six carbon atoms from the reaction products.

7. Process for making die es which comprises passing a vaporous mixture? containing a saturated monocarbonyl compound having from two 0 three carbon atoms and a monohydric alcohpl having from two to ,three carbon atoms, over a. catalyst comprising silica gel promoted with tantalum oxide, and recovering a die'ne having from four to six carbon atoms from the reaction products. 1

8. Process'for making dienes which comprises passing a vaporous mixture, containing a satuto three carbon atoms and a monohydric alcohol having from two to three carbon atoms,

, rated monocarbonyl compound having trom two over a catalyst comprising silica gel promoted r with columbium oxide, and recoverin a diene having from four to six carbon atoms from the reaction products. 1'

9. Process for making butadiene which comprises passing a vaporous mixture containing acetaldehyde and ethanol over a. catalyst of the group consisting of the oxides and silicates of zirconium, tantalum and columbium.

10. Process for making butadiene which comprises passing a vaporous mixture containing acetaldehyde and ethanol over a catalyst of the 10 the molar ratio of ethanol to acetaldehyde in said mixture being greate t than" one.

12'. Process for making butadiene which comprises passing a vaporous mixture containing acetaldehyde and ethanol over a catalyst comprising silica gel promoted with tantalum oxide at a temperature of about C. to about 450 C., the molar ratio of ethanol to acetaldehyde in said mixture being greater than one.

13. Process for making butadiene which comprises passing a vaporous mixture containing acetaldehyde and ethanol over a catalyst comprising silica gel promoted with columbium oxide at a temperature of about 150 C. to about 450 C., the molar ratio of ethanol to acetaldehyde in said mixture being greater than one.

14. Process for making butadiene which com prises passing ethanol vapors over a copper catalyst to form a mixture containing ethanol and acetaldehyde, and thereafter passin a mixture containing ethanol and acetaldehyde obtained from this reaction at a temperature of about 150 C. to about 450 C. over a catalyst comprising silica gel promoted with tantalum oxide, [separating ethanol and acetaldehyde from the butadiene formed, and recycling the acetaldehyde and at least part of the separated ethanol over said p omoted silica gel catalyst.

5. Process for making butadiene which com-' prises passing ethanol vapors over a copper catalyst to form a mixture containing ethanol and acetaldehyde, and thereafter passing a mixture of ethanol and acetaldehyde obtained from this reaction sit a temperature of about 150 C. to about {150 over a catalyst comprising silica gel promoted with tantalum oxide, separating ethanol and acetaldehyde from the butadiene formed, and recycling the separated acetaldehyde and part of the separated ethanol over said promoted silica gel catalyst, and recycling part of the separated ethanol over the copper catalyst.

16. Process for making butadiene which comprises passing a vaporous mixture containing erotonaldehyde and a monohydric alcohol having at least One hydrogen atom attached to the carbinol carbonation over a catalyst of the group consisting of the oxides and silicates of zirconium, tantalum and columbium, and recovering butadiene from the reaction products.

17. Process for making butadiene which comprises passing a vaporous mixture of crotonaldehydeand ethanol at a temperature of about 150 'C. to about 400 C. over a. catalyst comprising w silica gel promoted with tantalum oxide, and recovering" butadiene and acetaldehyde from the reaction Fproducts. a

18. Process for making butadiene which comprises passing a vaporous mixture of crotbnaldehyde and ethanol at atemperature of about 150 (2. to about 400 C. over a catalyst comprising oxide at a temperature of about 375 C. to about Number Name t 50 C d thereafter removing butadiene f o 3 'Jaeger June 1933 the reaction products; ,4 43 Legg W June 6, 1922 WALTER J. TCUSSAINT. 5 FOREIGN PATENTS JESSE DUNN- Number Country Date 15:806 Great Britain July 2, 1914 REFERENCES CITED The Ionowing references are of record in the OTHER REFERENCES i V 0 Ostromyslenski, "New Methods of Preparing this patent 7 Erythrene," J. Soc. Chem. 1110.. 35. p. 69, No. 1

] A S S PATENTS j (1916). (Copy in 260-680.)

Number Y Name om Cumming at 9.1., "Systematio Organic Chemis- 13'823119 Maxfmpfl Sept. 4, 192a try." (1926), page 410, lines 25 et seq. (Copy in 3,297,424 Maximoff'etal Sept. 29, 1942 Division 6.)

'l I Certificate of Correction f Patent No. 2,421,361; I May 27, 194.".

l v VA LTER J. TOUSSAINT ET AL.

\ i It is hereby certified that error appears in the rinted peoification of the above numbered-patent requiring correction as follows: olumn 10, line 46, claim 16, for

"cnrboh ation rend carbon atom; and that the said Letters Patent should be read with thisplcorretion therein that the same may conform to the record of the case in the P tent Office.

Signed and seled M522 day of July, A. D. 1947.

LESLIE FRAZER,

First Assistant Commissioner of Patents.

oxide at a temperature of about 375 C. to about Number Name t 50 C d thereafter removing butadiene f o 3 'Jaeger June 1933 the reaction products; ,4 43 Legg W June 6, 1922 WALTER J. TCUSSAINT. 5 FOREIGN PATENTS JESSE DUNN- Number Country Date 15:806 Great Britain July 2, 1914 REFERENCES CITED The Ionowing references are of record in the OTHER REFERENCES i V 0 Ostromyslenski, "New Methods of Preparing this patent 7 Erythrene," J. Soc. Chem. 1110.. 35. p. 69, No. 1

A S S PATENTS j (1916). (Copy in 260-680.) Number Y Name om Cumming at 9.1., "Systematio Organic Chemis- 13'823119 Maxfmpfl Sept. 4, 192a try." (1926), page 410, lines 25 et seq. (Copy in 3,297,424 Maximoff'etal Sept. 29, 1942 Division 6.)

'l I Certificate of Correction L Patent No. 2,421,361; I May 27, 194.".

l 7 VA LTER J. TOUSSAINT ET AL.

\ i It is hereby certified that error appears in the rinted peoification of the above numbered-patent requiring correction as follows: olumn 10, line 46, claim 16, for

"cnrboh ation rend carbon atom; and that the said Letters Patent should be read with thisplcorretion therein that the same may conform to the record of the case in the P tent Office.

Signed and seled M522 day of July, A. D. 1947.

LESLIE FRAZER,

First Assistant Commissioner of Patents. 

